1. Field of the Invention
The present invention relates to a vibration-damping device for use in a vehicle, which reduces vibrations excited in vibrating members of the vehicle, and more particularly to a vehicle vibration-damping having a novel structure capable of exhibiting effective vibration-damping performance when being applied to vibrating members such as transmission cases, suspension arms, sub-frames, body panels, engine units, mount brackets, exhaust system components, and so forth.
2. Description of the Related Art
Conventional known means for reducing vibration that are problematic in vehicles, such as automobiles, includes: (1) mass dampers wherein masses are affixed to the vibrating members, (2) dynamic dampers wherein masses are connected to the vibrating member, and supported by, a spring, and (3) vibration-damping materials wherein sheet-shaped elastic materials are adhered to the surfaces of the vibrating members. However, the (1) mass dampers and (2) dynamic dampers not only have problems in that they require large masses, but also that the range of frequencies over which there is effective vibration-damping is narrow. Moreover, the (3) vibration-damping materials have a problem in that not only is a large adhesive surface area required, but the mass is large as well. Furthermore, the (2) dynamic damper and (3) vibration-damping materials have temperature dependencies in the vibration-damping effect, and hence there is a problem in that it is difficult to obtain the desired stability in the vibration-damping effect.
In order to address problems such as those described above, JP-A-2001-241493 and JP-A-2002-213423, for example, disclose vibration-damping devices for vehicles of an attenuation-impact type wherein an independent mass member is disposed within a housing affixed to the vibrating member, with a gap of a specific size interposed therebetween, and without being adhesive to the housing, so that the independent mass can move relative to the housing. Upon input of vibrations, the independent mass member is forced to move relative to the housing in the vibration input direction to strike the housing through an elastic member, whereby vibration-damping effect is obtained through the use of energy loss due to sliding friction and collision when there are impacts between the independent mass member against the housing. This type of vehicle vibration-damping device affords the advantage of smaller mass when compared to the various types of conventional vibration-damping devices described above (such as the dynamic damper), but also that it is possible to obtain excellent vibration-damping effect relative to many different and broad ranges of vibration through tuning the resonant frequency of the vibration-damping device by appropriately changing the settings of, for example, hardness or modulus of elasticity of the elastic member, or the gap between the elastic member and either the mass member or the housing, depending on the resonant frequency of the objective vibrating member for which the vibration is to be controlled.
However, in recent years, this type of attenuation impact-type vibration-damping device for automobiles have been subjected to calls for even more sophisticated anti-vibration characteristics. In particular, there are cases wherein there are calls for improvements in the vibration-damping effects for vibrations in even higher frequency bands.
With this regards, the extensive studies conducted by the inventors have discovered that the attenuation impact-type vibration-damping device described above suffers from a problem that the vibration-damping effect is greatly reduced for vibrations in high frequency bands higher than the resonant frequency at which the independent mass member undergoes jumping displacement relative to the housing.
In order to cope with these problems, one may consider, for example, increasing the spring constant of the elastic member at the striking part of the mass member against the housing to increase the resonant frequency of the independent mass member. However, in order to increase the resonant frequency to several hundred hertz or above, the elastic member will be extremely hard, due to the increase in the spring constant of the elastic member. This results in a tendency for the striking noise and the shock to be problematic when the elastic member strikes the housing, and thus this is not always an effective approach.